1. Technical Field
The present disclosure relates to thermoacoustic devices, loudspeakers and, particularly, to a thermoacoustic device having flexible fasteners and a loudspeaker using the same.
2. Description of Related Art
Thermoacoustic effect is a conversion of heat to acoustic signals. The thermoacoustic effect is distinct from the mechanism of the conventional speaker, which the pressure waves are created by the mechanical movement of a diaphragm. When signals are input into a thermoacoustic element, heat is produced in the thermoacoustic element according to the variations of the signal and/or signal strength. Heat is propagated into surrounding medium. The heating of the medium causes thermal expansion and produces pressure waves in the surrounding medium, resulting in sound wave generation. Such an acoustic effect induced by temperature waves is commonly called “the thermoacoustic effect”.
A thermophone based on the thermoacoustic effect was created by H. D. Arnold and I. B. Crandall (H. D. Arnold and I. B. Crandall, “The thermophone as a precision source of sound”, Phys. Rev. 10, pp22-38 (1917)). They used platinum strip with a thickness of 7×10−5 cm as a thermoacoustic element. The heat capacity per unit area of the platinum strip with the thickness of 7×10−5 cm is 2×10−4 J/cm2*K. However, the thermophone adopting the platinum strip, heard in the open air, sounds extremely weak because the heat capacity per unit area of the platinum strip is too high.
Carbon nanotubes (CNT) are a novel carbonaceous material having extremely small size and extremely large specific surface area. Carbon nanotubes have received a great deal of interest since the early 1990s, and have interesting and potentially useful electrical and mechanical properties, and have been widely used in a plurality of fields. Fan et al. discloses a thermoacoustic device with simpler structure and smaller size, working without the magnet in an article of “Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers”, Fan et al., Nano Letters, Vol.8 (12), 4539-4545 (2008). The thermoacoustic device includes a sound wave generator which is a carbon nanotube film. The carbon nanotube film used in the thermoacoustic device has a large specific surface area, and extremely small heat capacity per unit area that make the sound wave generator emit sound audible to humans. The sound has a wide frequency response range. Accordingly, the thermoacoustic device adopted the carbon nanotube film has a potential to be used in place of the loudspeakers of the prior art.
However, the carbon nanotube film is electrically supported by two electrodes, and the carbon nanotube film will generate heat during operation and the electrodes will be heated and deformed in a direction perpendicular to an axis direction of the electrodes due to expansion caused by the heating. The deformation of the electrodes in the direction perpendicular to the axis direction can possibly cause deformation or breakage of the carbon nanotube film.